This study explored how senior high school students apply their conceptual knowledge, consisting of theoretical and system knowledge, to think critically when confronted with technological issues. We employed a curriculum on the history of communication technology to teach students about basic concepts in communication technology and to cultivate their ability to use critical thinking to confront issues in this domain. Concept mapping was adopted to assess students' ability to apply conceptual knowledge to their actual cognitive activities, and a critical thinking test was developed to evaluate students' performance in this regard. The sample consisted of 98 tenth-grade students. We used descriptive statistics, measures of relationships, and qualitative analyses to examine the data. The results indicated that, during the teaching of conceptual knowledge, most students easily fall victim to misconceptions about concepts that they cannot specifically observe in their own experiences and thus find it difficult to construct complete and correct knowledge. Although students' critical thinking about technological issues was positively correlated with their application of conceptual knowledge, their incomplete system knowledge could affect their ability to identify core problems of technological issues, and incorrect theoretical knowledge could influence their abilities to interpret information, thereby affecting their judgments.